I found different interesting news stories this morning. It looks like Google will slowly switching over to HTML5 for browser extensions like Offline support:

The Google spokesman wrote to clarify in a follow-up e-mail, "We're continuing to support Gears so that nothing breaks for sites that use it. But we expect developers to use HTML5 for these features moving forward as it's a standards-based approach that will be available across all browsers."

If Offline Gmail is ported to HTML5 then this is terrific news for Snow Leopard users. WebKit already has a pretty complete HTML5 implementation. In fact: Offline Gmail on the iPhone is already powered by it.